Flow cytometry provides a method of detecting and analyzing cells or particles contained in a sample, for example, blood cells in blood such as red blood cells (erythrocytes), white blood cells (leukocytes) and blood platelets (thrombocytes), or material components in urine such as bacteria, blood cells, epithelial cells or casts. These cells or material components may increase or decrease in number responsive to onset or progression of a disease. Accordingly, a disease can be diagnosed by detecting the status of each cell or material component on the basis of information about granules or particles in the sample.
Flow cytometer measures the number of cells and detects the number of a specific type of cells by optical processes such, as light scattering and fluorescence measurement, as the cells travel in suspension one by one passing a sensing point. Some flow cytometers from well-known vendors such as Beckman-Coulter or Becton Dickenson are expensive, with the cost ranging from $75,000-$125,000 which limits their availability to large reference laboratories. In addition to the initial cost of the instrument, service contracts for these instruments are typically 10% of the cost of the instrument on an annual basis. In addition, the sample volumes are usually large, such as in the 100 microliter range, and the necessary reagent volumes are correspondingly expensive.
For example, in the field of HIV treatments, an important parameter for determining disease staging is the number of CD4+ T cells (unit of cells/mm3) in peripheral blood. However, the laboratory evaluation of CD4+ T cell numbers can be cumbersome and expensive. Typically, the total lymphocyte count is determined by a routine CBC (complete blood count) assay, the percentage of CD4+ T lymphocytes as a function of total lymphocytes is determined by flow cytometry, and these values are multiplied to determine an absolute CD4+ T cell number. This analysis is expensive, time consuming and generally not locally available for less wealthy regions of the United States and the world.
Many clinical applications require frequent blood tests to monitor patients' status and the therapy effectiveness. It is highly desirable to use only small volume blood samples from patients for each test. Furthermore, it is highly desirable to have affordable and portable flow cytometry instruments for field applications, point-of-care applications and applications in resource-limited locations. Recently, efforts have been made to apply microfluidic technologies to flow cytometric analysis of cells to attempt to manufacture small sized portable flow cytometers.